Ben Waggoner

The Ediacaran Biotas in Space and Time

Abstract The “Ediacaran organisms,” which preceded and overlapped the Cambrian radiation of metazoans, include many fossils whose systematic positions remain contentious after over fifty years of study. It might seem that nothing particularly useful can be learned from a biota full of oddballs. However, analyses of the distribution of the Ediacaran organisms in time and space can be carried out without having to guess at the systematic position of the organisms. Combining these results with data on paleotectonics, paleoenvironmental parameters, and the ages of various assemblages sheds light on the origins, ecology, and even the systematic positions of the Ediacaran organisms. Parsimony Analysis of Endemism (PAE) confirms earlier studies in grouping Ediacaran biotas into three major clusters: the Avalon, White Sea, and Nama Assemblages. The available radiometric and stratigraphic data suggest that the Avalon is the oldest, the White Sea is next oldest, and the Nama extends to the base of the Cambrian. The “frondlike” Ediacaran taxa, and to a lesser extent the “medusoids,” collectively show significantly longer stratigraphic ranges, broader geographical and paleoenvironmental ranges, and less provinciality than “bilaterian” and tubular taxa. Almost all tubular Ediacarans appear to be confined to equatorial areas, whereas other Ediacaran organisms show weak or no latitudinal diversity gradients. I conclude that the Ediacaran organisms show a diverse range of responses to various environmental parameters. There is no basis for classifying them all as having a single body plan and mode of life, as has often been done in the past.

A fungal analog for newfoundland ediacaran fossils

Abstract We propose that some of the more conspicuous Ediacaran fossils from the Avalon Peninsula of Newfoundland, including Aspidella, Charnia, and Charniodiscus, were biologically similar to members of the Kingdom Fungi. These organisms were multicellular or multinuclear, lived below the photic zone, could not move or defoul themselves, did not exhibit taphonomic shrinkage, and were not transported or moved. Aspidella, in particular, appears to exhibit indeterminate growth without a maximum size constraint, and appears to show growth zonations similar to modern mycelia. Other fossils from this deposit exhibit a fractal-like growth pattern. Together, these features falsify algal, lichen, and metazoan interpretations of these fossils, yet reflect characteristics of modern fungal mycelia. We emphasize that although no Mistaken Point fossil appears to be a metazoan, not all of the Mistaken Point taxa, and not all of the Ediacaran organisms in general, can reasonably be interpreted using a fungal analogy. Furthermore, the hypothesis that these fossils were functionally fungus-like need not imply that the organisms were members of the crown-group Fungi. We propose further tests for evaluating both this functional hypothesis and the phylogenetic hypothesis that these organisms were members of the total-group Fungi.

EDIACARAN FOSSILS FROM THE SOUTHWESTERN GREAT BASIN, UNITED STATES

Abstract Ediacaran fossils from the southwestern Great Basin may help constrain regional Vendian-Cambrian biostratigraphy and provide biogeographic links between facies in this region and elsewhere. Locally, trace fossils suggest the Vendian-Cambrian boundary occurs within or below the upper third of the lower member of the Wood Canyon Formation. Ediacaran soft-bodied and tubular fossils, including the frondlike fossil Swartpuntia and tubular, mineralized or agglutinated fossils similar to Archaeichnium, Cloudina, Corumbella, and Onuphionella occur in the lowermost Wood Canyon Formation. Discoidal forms referred to Nimbia occur in both the lowermost Wood Canyon Formation and the underlying strata of the Stirling Quartzite. These fossils occur directly below Lower Cambrian trace fossils, including Treptichnus pedum, and confirm the persistence of the Ediacaran biota to near the base of the Cambrian. These faunas may also help strengthen previously proposed correlation schemes between the two main facies belts of the southwestern Great Basin (the Death Valley and White-Inyo facies), because a nearly identical Vendian-lowest Cambrian succession of faunas occurs in both regions. Lastly, lack of cosmopolitan Ediacaran faunas in these strata suggests a paleobiogeographic link between the southwestern U.S. and southern Africa in Vendian time.

EARLY CAMBRIAN EDIACARAN-TYPE FOSSILS FROM CALIFORNIA

Abstract Ediacara-type fossils are rare in the southwestern United States, and Cambrian occurrences of soft-bodied Ediacaran-type fossils are extremely rare. We report both discoidal and frondlike fossils comparable to Ediacaran taxa from the western edge of the Great Basin. We describe one specimen of a discoidal fossil, referred to the form species ?Tirasiana disciformis, from the upper member of the Lower Cambrian Wood Canyon Formation from the Salt Spring Hills, California. Two fragmentary specimens of frond-like soft-bodied fossils are described from the middle member of the Lower Cambrian Poleta Formation in the White Mountains, California, and the upper member of the Wood Canyon Formation in the southern Kelso Mountains, California. On the basis of similarities with fossils from the lower member of the Wood Canyon Formation and from the Spitzkopf Member of the Urusis Formation of Namibia, these specimens are interpreted as cf. Swartpuntia. All fossils were collected from strata containing diagnostic Early Cambrian body and trace fossils, and thus add to previous reports of complex Ediacaran forms in Cambrian marine environments. In this region, Swartpuntia persists through several hundred meters of section, spanning at least two trilobite zones.

REDUCTIO AD ABSURDUM: TESTING THE EVOLUTIONARY RELATIONSHIPS OF EDIACARAN AND PALEOZOIC PROBLEMATIC FOSSILS USING MOLECULAR DIVERGENCE DATES

Abstract Many of the late Neoproterozoic “Ediacaran fossils” have been referred to the Cnidaria, often on the basis of vague or poorly known features. However, representatives of the living Chondrophorina (=Porpitidae, Hydrozoa), Pennatulacea (Anthozoa), and Coronatae and/or Stauromedusae (Scyphozoa) have all been identified in Ediacaran biotas, based on specific morphological features preserved in a number of specimens. These three cnidarian groups have plausible Paleozoic representatives as well, but many of their Paleozoic fossils are also somewhat problematic. We test these systematic hypotheses by using them to calibrate divergence dates across the Cnidaria, based on an extensive molecular phylogeny of extant cnidarians. In this reductio ad absurdum approach, if a calibration based on one interpretation of a problematic fossil yields a glaringly inconsistent age for a better-known clade, that interpretation is likely to be mistaken. We find that assuming the existence of Pennatulacea and Scyphozoa in the “Ediacara biota” places the root of the Cnidaria between 800 and 1,000 Ma, a figure which is, at least, not out of line with other molecular clock estimates. However, assuming the existence of the Chondrophorina in the Neoproterozoic, or anywhere in the Paleozoic, pushes the root of the Cnidaria back to between 1,500 and 2,000 Ga, which is considerably older than the oldest previous estimates for the origin of the Cnidaria. We suggest that the likeliest explanation is that chondrophorines were not present in the late Precambrian or Paleozoic. The Ediacaran and Paleozoic fossils previously interpreted as chondrophorines probably represent other taxa.

Fossil habrotrochid rotifers in Dominican amber

Flask-shaped microfossils are reported from bracts of a moss in Eocene-Oligocene amber from the northern Dominican Republic. These microfossils are identical with the thecae of certain living moss-dwelling rotifers in the genusHabrotrocha (Bdelloidea), which have previously been reported as fossils only from Holocene peat. What may be an egg and a rotifer body fossil are associated with these thecae and further support the identification of these fossils withHabrotrocha; the fossils are almost identical to extantH. angusticollis. The parthenogenetic bdelloid rotifers have a longer evolutionary history than was previously thought; habrotrochid rotifers seem to have persisted for 35 million years with very little change in morphology or ecological role.

NON-TRILOBITE ARTHROPODS FROM THE SILVER PEAK RANGE, NEVADA

Abstract Two non-trilobite arthropods are described from the Emigrant Formation (Lower Cambrian-Lower Ordovician) in the Silver Peak Range, Esmeralda County, Nevada. A Middle or Upper Cambrian “arachnomorph” arthropod with a phosphatic exoskeleton has been noted in previous faunal lists, but has not been previously described. This fossil is here named Quasimodaspis brentsae gen. et sp. nov. Q. brentsae belongs in the Aglaspidida, a close outgroup to the true chelicerates; this is the second report of an aglaspidid from the Great Basin. Esmeraldacaris richardsonae gen. et sp. nov. is a newly discovered arthropod from the lower Ordovician, from beds transitional between the Emigrant Formation and the overlying Palmetto Formation. It is a survivor of an early arthropod lineage that does not belong in any extant taxon, but which may also include the Ordovician Corcorania and the Cambrian Mollisonia.